As MOSFET channel lengths are scaled down to sub-0.1 .mu.m dimensions and as the gate oxide thickness is scaled down to below 1.5 nm, tunneling currents larger than 1 A/cm.sup.2 will preclude the use of SiO.sub.2 as a gate dielectric layer. Therefore, the development of a Complementary Metal Oxide Semiconductor (CMOS) technology which utilizes a high-k gate insulator is a must for the continuing of CMOS scaling into the sub-0.1 .mu.m regime.
In conventional gate CMOS technologies wherein high-k gate insulators are employed, the activation anneal of the source/drain implants is typically performed after the gate insulator is formed. This limits the anneal temperature to less than 800.degree. C. to prevent degradation of the properties of the high-k insulator. Such low temperature anneals result in partial activation of the source/drain junctions as well as in depletion of the polysilicon gate. Both of the above mentioned characteristics are undesirable since they oftentimes lead to device performance degradation.
Moreover, in conventional gate CMOS technologies, the source/drain extensions must overlap the gate region of the device. This overlap causes capacitance in the device. The greater the overlap of the source/drain extensions with the gate region, the greater the overlap capacitance is. Likewise, if the overlap of the source/drain extensions with the gate is too small, an unreliable MOSFET device may be fabricated.
Another problem associated with conventional gate-CMOS technologies is that the gate is fabricated utilizing lithography and etching. The use of lithography and etching in forming the gate region of the CMOS device provides a MOSFET device whose channel length is in the same order as the lithographic tool. That is, lithography-defined gate length preclude the formation of sub-lithographic devices.
In view of the drawbacks with prior art gate CMOS technologies, there is a continued need to develop new and-improved methods that will permit the fabrication of MOSFET devices that have a high-k gate insulator, low overlap capacitance and a sub-lithographic channel length.